Integrated Multi-Radio Access Technology Multi-Frequency Admission Control

ABSTRACT

A node of a multiple radio access technology (multi-RAT) system acquires resource status information associated with each RAT of the multi-RAT system. The resource status information of the RATs of the multi-RAT system can be acquired by sniffing higher layer protocol information pertaining to call setup requests and/or call terminated messages. The node further maintains a flag representing overall resource availability associated with the RATs of the multi-RAT system, based on the acquired resource status information, for use in admission control and/or load balancing. The flag is associated with a pre-defined set of overall resource availability states of the multi-RAT system, where the availability states are defined in terms of admission control decisions.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/133,819, filed 9 Jun. 2011, which was the National Stage ofInternational Application No. PCT/SE2008/051433, filed 10 Dec. 2008, thedisclosures of each of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

Implementations described herein relate generally to radio accesstechnology systems and, more particularly, to admission control inmulti-radio access technology systems.

BACKGROUND

Admission control (AC) is a well-known and widely used radio resourcemanagement (RMM) function in a wide range of wireless access networks,including the Global Standard for Mobile (GSM) communications, theGeneralized Packet Radio Service (GPRS), the Enhanced Data for GSMEvolution (EDGE), the wide-band code division multiple access (WCDMA)and the evolved Universal Terrestrial Radio Access (E-UTRA) wirelessaccess networks. In general, admission control has the task to admit orreject a service request based on the available resources at the time ofthe service request and the resources that are needed to ensure properquality for the particular service. For example, for WCDMA networks,admission control takes into account multi-cell radio resources ratherthan basing the admission control on the state of a single radio cell.

The capacity of wireless networks that include multiple radio accesstechnologies (RATs) is a closely related and well-studied area.Multi-RAT networks are often characterized by an associated capacityregion that jointly characterizes the number of different services thatcan be accommodated by the multi-RAT system.

Load balancing is a radio resource management (RRM) technique that isoften used in multi-RAT networks. The purpose of load balancing is toassign or re-assign radio access technologies to in-progress sessionssuch that the overall radio resources are well utilized and thereby theoverall capacity of the multi-RAT system is maximized under some qualityof service or other constraint(s).

A well-known trade off in wireless networks, which is closely related toadmission control, occurs between the blocking of newly arriving servicerequests and the dropping of on-going services. This trade off can beexpressed as, the higher the number of in-progress sessions there is,there is an increased likelihood that some services need to be droppeddue to insufficient resources or outages. At an extreme case, systemswithout any admission control are feasible as long as it is acceptablethat certain sessions might need to be terminated prematurely in orderto ensure system stability and maintain some service quality fornon-dropped sessions.

The 3^(rd) Generation Partnership Project (3GPP) is currently finalizingRelease 8 of the Long Term Evolution (LTE) standards suite. LTE networksare expected to be deployed in the coming years by incumbent as well asgreen-field operators. As such, it is expected that LTE systems willoften be deployed as part of an operating multi-access infrastructure.In such situations, the LTE radio access equipments will typically beintegrated into operating with GSM/GPRS/EDGE/WCDMA systems.

There are two possible arrangements according to which a LTE basestation can be deployed in conjunction with other RATs: co-located basestations and base stations with mixed technologies. With co-located basestations, LTE system requirements are co-located with the equipments ofother RATs, possibly sharing some parts of the existing siteinfrastructure including power supply, transport networks, cellulartower, etc. In this type of deployment scenario, the set of equipment ofeach RAT is independent, although there can be some coordination on thelevel of various protocol layers.

With base stations having mixed technologies, the radio equipment usedby the base stations are commonly used by all RATs (e.g., LTE, UTRAN,GSM, etc.). It might also be possible to share the base band processingpart of the equipment. However, the higher layers operate independently.The primary benefit of a mixed technology base station is that it iscost efficient due to the use of only a single radio part. Thisquasi-integrated solution also makes the overall base station morecompact and power efficient thereby also reducing the operating cost ofnetwork and site maintenance. Presently, the mixed technology basestation is undergoing a rudimentary phase of standardization in variousstandardization bodies, which include GERAN and 3GPP RAN4.

SUMMARY

Exemplary embodiments described herein provide a technique forperforming admission control in a multi-RAT system that takes intoaccount an overall system traffic load across all of the RATs of themulti-RAT system. In exemplary embodiments, cross-layer cross-RATcommunication may be used to determine and aggregate load informationacross the RATs of the multi-RAT system. A global flag may be set, basedon the determined overall load information, and used for multi-RATadmission control (MRAC) decisions with respect to future servicerequests associated with UEs requesting service access. Use of theglobal flag, as described herein, enables a service request arriving ata RAT of the multi-RAT system to be admitted regardless of the servicerequirement as long as there are sufficient resources in the overallsystem. Therefore, the RAT receiving the service request may not need toexecute any admission control even if the free resources in the RATalone would normally make it necessary to examine the service requestand make an assessment whether the service request can be executed ornot.

According to one aspect, a method implemented in a node of a multi-radioaccess technology (RAT) system may include acquiring resource statusinformation associated with each RAT of the multi-RAT system. The methodmay further include maintaining a flag representing overall resourceavailability associated with the RATs of the multi-RAT system, based onthe acquired resource status information, for use in admission controland/or load balancing.

According to a further aspect, a node in a multiple radio accesstechnology (multi-RAT) system may include a resource status acquisitionunit to acquire resource status information associated with each RAT ofthe multi-RAT system and a flag maintenance unit to maintain a flagrepresenting resource availability associated with multiple RATs of themulti-RAT system based on the acquired resource status information. Thenode may further include one or more units to perform admission controlfor system access requests, or to perform load balancing of systemaccess requests across the RATs of the multi-RAT system, based oncontents of the flag.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description, explain thepresent disclosure. In the drawings:

FIG. 1A illustrates an exemplary environment in which a user equipmentmay communicate with another device via a network(s) that includes amulti-RAT system;

FIG. 1B illustrates an exemplary implementation of the network of FIG.1A, where the multi-RAT system includes an LTE RAT, a WCDMA RAT and aGSM RAT;

FIG. 1C illustrates exemplary details of the LTE RAT of FIG. 1B;

FIG. 2A depicts co-located base stations having multiple RATs in theexemplary implementation of FIG. 1B;

FIG. 2B depicts a single base station that deploys multiple RATs in theexemplary implementation of FIG. 1B;

FIG. 3 depicts an exemplary implementation in which cross-layercommunication may be used to collect resource status information in aradio base station of a main RAT of the network of FIG. 1B;

FIG. 4 illustrates exemplary components of the UE of FIG. 1A;

FIG. 5 illustrates an exemplary implementation of a base station thatmay correspond to an eNodeB of FIG. 1C;

FIG. 6 depicts functional components of a RAT node that may correspondto an eNodeB of the LTE RAT of FIG. 1B;

FIG. 7 depicts an exemplary global flag that may be used to indicate theoverall resource availability of the multiple RATs of the network(s) ofFIG. 1A;

FIG. 8 is a flowchart that illustrates an exemplary process foracquiring resource status information associated with each RAT of amulti-RAT system;

FIG. 9 is a flowchart that illustrates an exemplary process fordetermining overall resource availability and for performing admissioncontrol in the multi-RAT system based on the determined overall resourceavailability; and

FIG. 10 is an exemplary messaging diagram associated with the exemplaryprocess of FIG. 9.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings.The same reference numbers in different drawings may identify the sameor similar elements. Also, the following detailed description does notlimit the present disclosure.

In a multi-RAT system, a service access request can be granted as longas there is a sufficient amount of resources for the service availablein the entire system. An admission decision granting the service accessshould be based on an up-to-date resource estimation and, therefore,resource availability estimates need to be made available with minimaldelay and signaling overhead. A multi-RAT admission control (MRAC)system should be able to achieve the following:

1) ensure service quality for on-going and newly accepted sessions;

2) minimize call blocking probability (e.g., avoiding false rejectdecisions);

3) minimize call/session drops (e.g., avoiding false accept decisions);

4) ensure a low delay between a service request and an admission controldecision;

5) take into account user service class (e.g., subscription), servicecharacteristics (e.g., GBR/non-GBR), user preferences with respect toblocking/dropping rates, and preferred RAT (if any); and

6) make efficient use of overall radio and other radio networkresources.

In addition to the requirements listed above, the MRAC procedure shouldremain as low complexity as possible and preferably should not assume acentralized multi-RAT entity to avoid new physical network elements,reduce signaling overhead and avoid the need for standardizing newinterfaces or protocols or signaling messages.

Exemplary embodiments described herein satisfy the above-notedrequirements by maintaining a single flag that indicates whether theoverall multi-RAT system is such that admission control in one of theRATs (e.g., the LTE system) does not have to be exercised at all. Thus,exemplary embodiments may avoid using admission control as long aspossible in order to simplify the service setup and to ensure low delay.A service request arriving at one of the RATs (e.g., the LTE RAT) may beadmitted irrespective of the service requirement as long as there aresufficient resources in the overall multi-RAT system. Therefore, a RATreceiving a service request (e.g., the LTE system) may not need toexecute any admission control procedure even if the free resources inthe one RAT alone would make it necessary to examine the service requestand make an assessment whether the service request can be executed ornot. Exemplary embodiments facilitate the elimination of admissioncontrol by a flag that aggregates overall current load information. Theflag may be maintained in a “main” RAT (e.g., the LTE RAT) of themulti-RAT system using cross-layer cross-RAT communication. Ameasurement based MRAC for the entire multi-RAT system may take intoaccount the amount of resources available in the entire system andconsider service requirements and user preferences. The resourceavailability information may be maintained in the flag stored in one ofthe system RATs (e.g., the main RAT). The flag may be used whendetermining resource availability and when exercising MRAC for serviceaccess requests.

In further implementations described herein, a UE preference regardingwhether the UE prefers to go through MRAC may be sent with the servicerequest that requests system service for the UE. The UE preference mayindicate whether the UE prefers to undergo admission control or not.Additionally, a RAT selection preference may be sent within the servicerequest that requests system service for the UE. The RAT selectionpreference may indicate whether RAT re-selection is acceptable for theservice request or not. The determination of whether to perform MRAC forthe service request, or whether to perform RAT selection/re-selection,may be based on the MRAC preference or the RAT selection preference.

The terms “communication system” and “network” may be usedinterchangeably throughout this description. The term “RAT” is intendedto be broadly interpreted to include any type of wireless accesstechnology. For example, the wireless access technology may be based ona radio access technology (e.g., General Packet Radio Service (GPRS),LTE, GSM, etc.), a microwave access technology (e.g., Bluetooth,Worldwide Interoperability for Microwave Access (WiMAX), Institute ofElectrical and Electronic Engineering (IEEE) 802.X, etc.), and/or asatellite access technology.

FIG. 1A illustrates an exemplary environment 100 in which a userequipment (UE) 110 may communicate with another device 120 via anetwork(s) 130. Network(s) 130 may include one or more networks of anytype, including, for example, a local area network (LAN); a wide areanetwork (WAN); a metropolitan area network (MAN); a telephone network,such as a PSTN or a PLMN; a satellite network; an intranet, theInternet; or a combination of networks. The PLMN(s) may further includea packet-switched sub-network, such as, for example, a General PacketRadio Service (GPRS) network, a Cellular Digital Packet Data (CDPD)network, or a Mobile IP network. As shown in FIG. 1A, network(s) 130 mayinclude a multi-RAT system that includes multiple, different RATs,including RATs 140-1 through 140-N. One or more of RATs 140-1 through140-N may be used by UE 110 for communicating with device 120. Each ofRATs 140-1 through 140-N may include, for example, an evolved UniversalMobile Telecommunications System Terrestrial Access Network (E-UTRAN)FDD RAT, an E-UTRAN Time Divisional Duplexing (TDD) RAT, a Wide BandCode Division Multiple Access (WCDMA) RAT, an advanced E-UTRAN TDD RAT,an advanced E-UTRAN Frequency Division Duplexing (FDD) RAT, a UTRAN TDDRAT, a high rate packet data (HRPD) RAT, a Global System for MobileCommunications (GSM) RAT, a cdma2000 RAT, or other types of RATs. Insome exemplary implementations, one of RATs 140-1 through 140-N mayserve as a “main” RAT in which one of the nodes of the main RAT maymaintain a flag that indicates an overall status of resources in themulti-RAT system.

UE 110 may include a cellular radiotelephone, a personal digitalassistant (PDA), a Personal Communications System (PCS) terminal, alaptop computer, a palmtop computer, or any other type of device orappliance that includes a communication transceiver that permits thedevice to communicate with other devices via a wireless link. A PCSterminal may combine a cellular radiotelephone with data processing,facsimile and data communications capabilities. A PDA may include aradiotelephone, a pager, an Internet/intranet access device, a webbrowser, an organizer, calendars and/or a global positioning system(GPS) receiver. UE 110 may be referred to as a “pervasive computing”device.

Device 120 may include a similar device to UE 110 and, in someimplementations, may additionally include a telephone (e.g., Plain OldTelephone system (POTs) telephones) that is connected to a PublicSwitched Telephone Network (PSTN).

FIG. 1B depicts an exemplary implementation of network(s) 130 in whichRAT 140-1 includes an LTE RAT, RAT 140-2 includes a WCDMA RAT and RAT140-3 includes a GSM RAT. LTE RAT 140-1 may include a Long TermEvolution RAT. WCDMA RAT 140-2 may include a Wide-band Code DivisionMultiple Access RAT. GSM RAT 140-3 may include a Global System forMobile communications RAT. Network(s) 130 may include different,additional, and/or fewer RATs than those shown in FIG. 1B.

FIG. 1C illustrates exemplary details of LTE RAT 140-1 of network 130.LTE RAT 140-1 may include evolved NodeB (eNodeB) nodes, MobilityManagement Entity (MME) nodes, and Serving Gateway (S-GW) nodes, allconnected to a transport network 150. As depicted in FIG. 1C, LTE RAT140-1 may include eNodeBs 160-1 through 160-P, S-GWs 170-1 through 170-Nand MMEs 180-1 through 180-M. eNodeBs 160-1 through 160-P may includeLTE base station nodes that serve as intermediate nodes for UEscommunicating with other devices. For example, FIG. 1C depicts eNodeB160-1 serving as an intermediate node for UE 110 to communicate withanother node (not shown). ENodeBs 160-1 through 160-P may communicatewith UEs via a wireless interface and may then transfer thosecommunications towards a destination node or device (e.g., towardsdevice 120) via transport network 150.

S-GWs 170-1 through 170-N may include logical nodes that terminate UEconnections (called “EPS bearers” in 3GPP terminology). An EPS bearermay include a connection provided by the SAE/LTE system in between theUE and the outside network (e.g., the Internet). S-GWs 170-1 through170-N may additionally each include Packet Data Network Gateway (P-GW)functionality and the P-GW may allocate an IP address to the UE toprovide the connection between the UE and the outside network.

MMEs 180-1 through 180-M may each include functionality for handling UEmobility within environment 100. For example, MME 180-1 may serve UE 110and MME 180-M may serve another UE (not shown).

Transport network 150 may include one or more networks of any type,including, for example, a local area network (LAN); a wide area network(WAN); a metropolitan area network (MAN); a satellite network; anintranet, the Internet; or a combination of networks. eNodeBs 160-1through 160-P, S-GWs 170-1 through 170-N, and MMEs 180-1 through 180-Mmay reside in an SAE/LTE network and may be connected via transportnetwork 150.

Two possible arrangements may be used for deploying multiple RATs inenvironment 100: 1) co-located base stations, each having a differentRAT; or 2) a single base station having mixed RAT technologies. Withco-located base stations, LTE system requirements may be co-located withthe equipments of other RATs, possibly sharing some parts of theexisting site infrastructure including power supply, transport networks,cellular tower, etc. In this type of deployment scenario, the set ofequipment of each RAT may be independent, though there may be somecoordination on the level of various protocol layers. In this approach,a new RAT can be easily added or an existing one can be removed orreplaced by another one.

With single base stations having mixed RAT technologies, the radioequipment used by the base stations may commonly be used by all RATs(e.g., LTE, UTRAN, GSM, etc.). It might also be possible to share thebase band processing part of the equipment. However, the higher layersmay operate independently. The primary benefit of a mixed RAT basestation is that it is cost efficient due to using only a single radioportion. This quasi-integrated solution also makes the overall basestation more compact and power efficient thereby also reducing theoperating cost of network and site maintenance.

FIG. 2A depicts co-located base stations 200 having multiple RATs. Eachof the co-located base stations 200 of FIG. 2A may include a differenttype of RAT. For example, as shown in FIG. 2A, co-located base stations200 may include a base station deploying an LTE RAT 210, a base stationdeploying a GSM RAT 220 and/or a base station deploying WCDMA RAT 230.Co-located base stations 200 may be located within close geographicproximity to one another.

FIG. 2B depicts a single base station 240 that deploys multiple RATs. Asshown in the illustrative example of FIG. 2B, base station 240 maydeploy an LTE RAT 240, a WCDMA 260 and/or a GSM RAT 270. Deployingmultiple RATs within a single base station, as shown in FIG. 2B, permitsthe use of integrated radio equipment (i.e., the same radio equipmentmay be used by all of the different RATs) and, additionally, permits theuse of combined radio resource management (RRM) techniques such as, forexample, admission control. The use of combined RRM techniques enablesthe system operator to make efficient use of overall radio resources inbase stations having mixed RATs. Base station 240 may, for example,include an eNodeB.

When multiple RATs are deployed at co-located base stations 200, shownin FIG. 2A, or at a single base station 240, shown in FIG. 2B, multi-RATcross-layer communication 300 may be used, as illustrated in FIG. 3, toenable the acquisition of the overall resource status information amongthe different RATs. In a multi-RAT system with co-located cells, theresource status information, such as, for example, number of activeusers, active radio bearers, active sessions, etc., may be available indifferent nodes. Such nodes may include, for example, BSC/CN for GSM,RNC/CN for UTRAN, BSC/CN for cdma2000, and eNodeB/CN for E-UTRAN. Evenin the case of a single base station deploying multiple different RATs,the resource status information may reside in different nodes because ofindependent higher protocol layers. In exemplary embodiments describedherein, cross-layer communication 300 may be used to acquire resourcestatus information from each of the different RATs. FIG. 3 depicts anexemplary implementation in which cross-layer communication 300 may beused to collect resource status information in a radio base station ofthe main RAT. For example, as shown in FIG. 3, an LTE eNodeB 310 maycollect resource status information from a WCDMA NodeB 320 and/or a GSMbase station 330. The resource status information may be obtained fromdifferent layers (e.g., RRC or NAS) by reading different protocols(e.g., SIP, RTP, etc.). Based on the collected resource statusinformation, MRAC for the entire multi-RAT system may be exercised by,for example, the LTE eNodeB 310.

The resource status information acquired via multi-RAT cross layercommunication 300 may include a total number of active sessions, callsor active radio bearers in each RAT. This information may be acquired bytracking (e.g., “sniffing”) higher layer protocol information related tocall setup requests and call terminated messages, such as, for example,SIP signaling. Such messages for each RAT may traverse a correspondingbase station and can be read by cross-layer examination. Duringcross-layer examination, packets of a certain protocol layer (e.g., SIP)may be inspected and relevant information may be fed to another protocollayer (e.g., MAC). This cross-layer communication can take place in anydirection (i.e., from higher layer to lower layer or vice versa).

For example, a total number of active calls at any time in one RAT canbe estimated by tracking all new call requests (N_(request)) and callreleases (N_(release)). Therefore, at any time T₁, the number of activecalls (N_(active)) in a RAT may be expressed by the followingexpression:

N _(active)(T ₁)=N _(active)(T ₀)+N _(request)(Δt)−N _(release)(Δt)

where Δt=T₁−T₀

The number of active calls may be tracked and maintained per servicetype, such as, for example, service types including narrow band,broadband, real time, non-real time, etc. Similarly, other performanceparameters (e.g., a number of active sessions or radio bearers) may betracked. The resource status information acquired via multi-RAT crosslayer communication 300 may further include an aggregate number of callsetup requests and/or an aggregate number of call terminated messages ineach of the RATs, a number of call setup requests per service typeand/or a number of call terminated messages per service type in each ofthe RATs, or a number of call setup requests per radio bearer typeand/or a number of call terminated messages per radio bearer type ineach of the RATs.

FIG. 4 illustrates exemplary components of UE 110. UE 110 may include atransceiver 405, a processing unit 410, a memory 415, an input device(s)420, an output device(s) 425, and a bus 430.

Transceiver 405 may include transceiver circuitry for transmittingand/or receiving symbol sequences using radio frequency signals via oneor more antennas. Processing unit 410 may include a processor,microprocessor, or processing logic that may interpret and executeinstructions. Processing unit 410 may perform all data processingfunctions for inputting, outputting, and processing of data includingdata buffering and UE control functions, such as call processingcontrol, user interface control, or the like.

Memory 415 may provide permanent, semi-permanent, or temporary workingstorage of data and instructions for use by processing unit 410 inperforming device processing functions. Memory 415 may include ROM, RAM,large-capacity storage devices, such as a magnetic and/or opticalrecording medium and its corresponding drive, and/or other types ofmemory devices. Input device(s) 420 may include mechanisms for entry ofdata into UE 110. For example, input device(s) 420 may include a key pad(not shown), a microphone (not shown) or a display unit (not shown). Thekey pad may permit manual user entry of data into UE 110. The microphonemay include mechanisms for converting auditory input into electricalsignals. The display unit may include a screen display that may providea user interface (e.g., a graphical user interface) that can be used bya user for selecting device functions. The screen display of the displayunit may include any type of visual display, such as, for example, aliquid crystal display (LCD), a plasma screen display, a light-emittingdiode (LED) display, a cathode ray tube (CRT) display, an organiclight-emitting diode (OLED) display, etc.

Output device(s) 425 may include mechanisms for outputting data inaudio, video and/or hard copy format. For example, output device(s) 425may include a speaker (not shown) that includes mechanisms forconverting electrical signals into auditory output. Output device(s) 425may further include a display unit that displays output data to theuser. For example, the display unit may provide a graphical userinterface that displays output data to the user. Bus 430 mayinterconnect the various components of UE 110 to permit the componentsto communicate with one another.

The configuration of components of UE 110 illustrated in FIG. 4 is forillustrative purposes only. Other configurations with more or fewercomponents, or a different arrangement of components may be implemented.

FIG. 5 illustrates an exemplary implementation of a base station 500that may correspond, for example, to an eNodeB 160 of FIG. 1C. Basestation 500 may include a transceiver 505, a processing unit 510, amemory 515, an interface 520 and a bus 525.

Transceiver 505 may include transceiver circuitry for transmittingand/or receiving symbol sequences using radio frequency signals via oneor more antennas. Processing unit 510 may include a processor, amicroprocessor, or processing logic that may interpret and executeinstructions. Processing unit 510 may perform all device data processingfunctions. Memory 515 may provide permanent, semi-permanent, ortemporary working storage of data and/or instructions for use byprocessing unit 510 in performing device processing functions. Memory515 may include read only memory (ROM), random access memory (RAM),large-capacity storage devices, such as a magnetic and/or opticalrecording medium and its corresponding drive, and/or other types ofmemory devices. Interface 520 may include circuitry for interfacing witha link that connects to an external network, such as, for example,transport network 150. Bus 525 may interconnect the various componentsof base station 500 to permit the components to communicate with oneanother.

The configuration of components of base station 500 illustrated in FIG.5 is for illustrative purposes only. Other configurations with more orfewer components, or a different arrangement of components may beimplemented.

FIG. 6 depicts functional components of a RAT node 600 that maycorrespond, for example, to an eNodeB 160 of LTE RAT 140-1. RAT node 600may, therefore, correspond to a node in the main RAT of network(s) 130.In other implementations, RAT node 600 may correspond to other nodes inLTE RAT 140-1, or to nodes in other RATs (e.g., WCDMA RAT or GSM RAT).RAT node 600 may include a resource status acquisition unit 605, aflag(s) maintenance unit 610, a flag(s) database 620, a resourceavailability evaluator 630, a multi-RAT admission control (MRAC) unit640, and a RAT selection unit 650.

Resource status acquisition unit 605 may obtain multi-RAT resourcestatus information from RATS (e.g., RATs 140-1 through 140-N of FIG.1A). Such resource status information may include, but is not limitedto, a total number of active sessions or calls in each RAT, a number ofactive radio bearers in each RAT, a number of active calls per servicetype in each RAT (e.g., narrow band service, broadband service, realtime service, non-real time service, etc.), an aggregate number of callsetup requests in each RAT, an aggregate number of call terminatedmessages in each RAT, a number of call setup requests per service typein each RAT, or a number of call terminated messages per service type ineach RAT.

Flag maintenance unit 610 may determine and maintain an N-bit globalflag indicating an overall resource situation of the multi-RAT system.In some implementations, flag maintenance unit 610 may also maintainlocal flags that indicate a resource situation of each single RAT of themulti-RAT system. The global flag and local flags are further describedbelow with respect to FIG. 7. Flag database 620 may store the globalflag and/or local flag(s) determined by flag maintenance unit 610.

Resource availability evaluator 630 may retrieve the global flag and/orlocal flag(s) from flag database 620 and may use the retrieved flag(s)as a basis for determining overall resource availability across themultiple RATs 140-1 through 140-N. MRAC unit 640 may use the overallresource availability across the multiple RATs, determined by resourceavailability evaluator 630, to make a decision whether to perform, ornot to perform, multi-RAT admission control. RAT selection unit 650 mayuse the overall resource availability across the multiple RATs,determined by evaluator 630, to select a RAT from the multiple RATs140-1 through 140-N to service a particular UE's service request.

FIG. 7 depicts an exemplary global flag 700 that may be used to indicatethe overall resource availability of the multiple RATs 140-1 through140-N of network(s) 130. A length of a global flag (e.g., global flag700) may be chosen with respect to a number of system states defined forthe multi-RAT admission control process. The set of possible systemstates (including the number of states) can be specified by the systemoperator by defining relevant overall resource thresholds and admissionconditions for selected service groups. For example, narrowband servicerequests may be served by all RATs. The set of possible system statesmay be defined in terms of admission control decisions that correspondto each of the possible system states. The pre-defined set of overallresource availability states of the multi-RAT specified by the globalflag may include one or more of the following:

-   -   a) unconditional acceptance of all services;    -   b) conditional acceptance of broadband guaranteed bit rate (GBR)        services and unconditional acceptance of all other services;    -   c) conditional acceptance of broadband GBR services, conditional        acceptance of narrowband GBR services and unconditional        acceptance of all other services; or    -   d) unconditional rejection of all services.

Returning to FIG. 7, exemplary global flag 700 depicts five differentpossible values for flag 700, each value represented by three bits, witheach value corresponding to a different one of several states 710. Flagvalue “000” 720 corresponds to a state 710 in which all service requestsare accepted. Flag value “001” 730 corresponds to a state 710 in whichadmission control may be performed only for broadband GBR services. Flagvalue “101” 740 corresponds to a state 710 in which admission controlmay be performed for broad and narrowband GBR services. Flag value “010”750 corresponds to a state 750 in which admission control may beperformed for all GBR sessions. Flag value “011” 760 corresponds to astate in which all GBR sessions are blocked.

The global flag (e.g., global flag 700) may be complied in the main RATbased on the load state and load information communicated by the otherRATs to the main RAT. In systems where not all RATs are capable ofsupporting all services, or not all users can be supported by all RATs,the global flag must account for all possible combinations of RATs(i.e., subsets of RATS that can be requested in the system). The globalflag may be recompiled directly upon receiving information from any ofthe RATs of the multi-RAT system without storing single RAT information.Alternatively, the single-RAT information can be used to maintain acorresponding local flag (one local flag may be maintained in the mainRAT for every RAT of the multi-RAT system).

Alternatively, the global flag can be recompiled on request if the mainRAT, in additional to the global flag, maintains a local flag for everyRAT of the multi-RAT system. The local flag may then be updated everytime the load information is obtained from the corresponding RAT. Theglobal flag may be complied periodically, or after triggering by anevent, based on the local flags for the RATs. The set of statesrepresented by the local flags can be the same for all RATs. Even inthis case, the same states may be defined differently in different RATsdepending on the specific technologies of the different RATs. When thesets of states for the local global states coincide, the global flag canbe determined as a result of the logical conjunction operation (orlogical “AND”) over all of the local flags.

FIG. 8 illustrates an exemplary process for acquiring resource statusinformation associated with each RAT of a multi-RAT system. Theexemplary process of FIG. 8 may be implemented by an eNodeB 160 of LTERAT 140-1 in an exemplary implementation in which LTE RAT 140-1 acts asa main RAT of a multi-RAT system. In other implementations, theexemplary process of FIG. 8 may be implemented in other nodes in LTE RAT140-1, or in other RATs of network 130 (e.g., WCDMA RAT 140-2 or GSM RAT140-3).

The exemplary process may begin with the acquisition of resource statusinformation for each RAT of the multi-RAT system (block 800). Resourcestatus acquisition unit 605 may obtain resource status informationassociated with each of RATs 140-1 through 140-N. Such resource statusinformation may include, for example, a total number of active sessionsor calls in each RAT, a number of active radio bearers in each RAT, anumber of active calls per service type in each RAT (e.g., narrow bandservice, broadband service, real time service, non-real time service,etc.), an aggregate number of call setup requests in each RAT, anaggregate number of call terminated messages in each RAT, a number ofcall setup requests per service type in each RAT, or a number of callterminated messages per service type in each RAT.

The acquired resource status information may be collected in a node of aRAT of the multi-RAT system (block 810). For example, resource statusacquisition unit 605 of eNodeB 160 of LTE RAT 140-1 may collect andstore the acquired resource status information in a memory. A local flagmay be updated for each RAT of the multi-RAT system based on acquiredresource status information for each respective RAT (block 820). Flagmaintenance unit 610 may analyze the resource status information foreach RAT obtained by acquisition unit 605 and may set the bits of alocal flag for each respective RAT. For example, if the obtainedresource status information for a given RAT indicates that the RAT iscurrently overloaded with traffic, then flag maintenance unit 610 mayset the local flag to a value (e.g., “011”) that indicates that allservice requests are to be rejected.

A global flag may be updated for the multi-RAT system based on thecollected resource status information and/or based on the local flagsfor each RAT (block 830). In one implementation, flag maintenance unit610 may use the local flags for each of the RATs to set the bits of theglobal flag. In another implementation, flag maintenance unit 610 maydirectly analyze the resource status information for each RAT obtainedby acquisition unit 605 and may set the bits of the global flag based onthe resource status information. For example, referring to global flag700 of FIG. 7, if an analysis of the resource status informationindicates that all service types can currently be handled by one or moreof RATs 140-1 through 140-N, then flag 700 may be set to a value of“000” 720 indicating that all service requests will be accepted.

FIG. 9 illustrates an exemplary process for determining overall resourceavailability and for performing admission control in the multi-RATsystem based on the determined overall resource availability. Theexemplary process of FIG. 9 may be implemented by an eNodeB 160 of LTERAT 140-1 in an exemplary implementation in which LTE RAT 140-1 acts asa main RAT of a multi-RAT system. In other implementations, theexemplary process of FIG. 9 may be implemented by other nodes in LTE RAT140-1 or in other RATs of network 130 (e.g., WCDMA RAT 140-2 or GSM RAT140-3).

The exemplary process may begin with the receipt of a bearer requestassociated with a UE (block 900). As shown in FIG. 10, a bearer request1000 associated with an attempt to connect a call or to establish asession for UE 110 may be forwarded from a service layer via, forexample, an S-GW 170 to an MME 180 associated with UE 110. Bearerrequest 1000 may include an admission control preference indicatorand/or a RAT selection preference indicator. The AC preference indicatormay indicate whether the UE prefers to go through MRAC or wants to avoidMRAC. The AC preference indicator provides flexibility to UE users inchoosing whether to go through MRAC or not. The RAT selection preferenceindicator may indicate whether RAT selection and redirection isacceptable for the bearer request or not. System operator control overthese user preferences can be implemented, for example, by means of aflexible charging policy. The AC preference indicator and the RATselection preference indicator may be completely transparent to the UEand the user. Based on receipt of bearer request 1000, MME 180 mayforward a bearer setup request 1005 to eNodeB 160 that includes the ACpreference indicator and/or the RAT selection preference indicator.

A determination may be made whether the UE associated with the bearerrequest prefers to avoid admission control (block 910). eNodeB 160 mayinspect a received bearer setup request (e.g., bearer setup request1005) to determine if the AC preference indicator indicates that thecorresponding UE prefers to avoid admission control. If so (YES—block910), then a RAT may be selected from the multiple RATs withoutperforming admission control (block 920). If eNodeB 160's inspection ofthe AC preference indicator identifies that the UE prefers to avoidadmission control then, in one exemplary embodiment, the UE may begranted access without performing admission control. In anotherexemplary embodiment, if eNodeB 160's inspection of the AC preferenceindicator identifies that the UE prefers to avoid admission control,then eNodeB 160 may inspect the RAT selection preference indicator toidentify if RAT re-selection is acceptable for this UE. If RATre-selection is acceptable, then eNodeB 160 may select any of RATs 140-1through 140-N for handling the call/session request from the UE. If,according to the RAT selection preference indicator, RAT re-selection isunacceptable for this UE, then a default RAT may be selected for the UE.FIG. 10 depicts bearer setup request 1005 being received at eNodeB 160.eNodeB 160 may inspect the AC preference indicator and RAT selectionpreference from the bearer setup request 1005 to determine if the UEprefers to avoid admission control. If the AC preference indicatoridentifies that the UE prefers to avoid admission control, eNodeB 160may skip MRAC 1010 and may continue the access granting process bysending a radio bearer setup message 1015 to UE 110.

If the UE does not prefer to avoid admission control (NO—block 910),then an overall resource availability may be determined across themultiple RATs based on the global flag or multiple local flags (block930). eNodeB 160 may inspect the AC preference indicator to identifywhether the UE prefers to not avoid admission control. If the ACpreference indicator indicates that the UE does not prefer to avoidadmission control, then resource availability evaluator 630 of eNodeB160 may retrieve the global flag or multiple local flags from flagdatabase 620. By inspecting the bit values of the retrieved global flag,resource availability evaluator 630 may identify the resourceavailability states of the multi-RAT system in terms of admissioncontrol decisions. For example, if global flag 700 indicates a value of“001” 730, then resource availability evaluator 630 may determine thatadmission control should be performed for service requests associatedwith broadband GBR services.

Admission control may be selectively performed or not performed for theUE based on the determined resource availability across the multipleRATs (block 940). A number of admission control actions may be performedbased on the resource availability identified by the global flag (orlocal flags). The admission control actions identified by inspection ofthe global flag may include, but are not limited to, the following:

-   -   a) unconditional acceptance of all services;    -   b) conditional acceptance of broadband guaranteed bit rate (GBR)        services and unconditional acceptance of all other services;    -   c) conditional acceptance of broadband GBR services, conditional        acceptance of narrowband GBR services and unconditional        acceptance of all other services; or    -   d) unconditional rejection of all services.

A RAT may be selected from the multiple RATs to service the UE based onthe determined resource availability across the multiple RATs (block950). eNodeB 160 may inspect the RAT selection preference indicator toidentify if RAT re-selection is acceptable for this UE. If RATre-selection is acceptable, then eNodeB 160 may select any of RATs 140-1through 140-N for handling the call/session request from the UE based onthe content of the call/session request (e.g., bearer setup request) andbased on the determined resource availability. If, according to the RATselection preference indicator, RAT re-selection is unacceptable forthis UE, then a default RAT may be selected for the UE. FIG. 10 depictsbearer setup request 1005 being received at eNodeB 160. eNodeB 160 mayinspect the RAT selection preference from the bearer setup request 1005and may continue the access granting process by sending a radio bearersetup message 1015 to the UE 110. As further shown in FIG. 10, eNodeB160 and UE 110 may engage in radio bearer setup establishment 1020.Subsequent to the radio bearer establishment 1020, UE 110 may return aradio bearer setup response 1025 to eNodeB 160 acknowledgingestablishment of the radio bearer setup. In turn, eNodeB 160 may returna bearer setup response message 1030 to MME 180 acknowledging radiobearer setup. MME 180 may further send a bearer response message 1035via a service layer to, for example, the appropriate S-GW 170.

The foregoing description of implementations provides illustration anddescription, but is not intended to be exhaustive or to limit thepresent disclosure to the precise form disclosed. Modifications andvariations are possible in light of the above teachings, or may beacquired from practice of the present disclosure. For example, while aseries of blocks has been described with regard to FIGS. 8 and 9, theorder of the blocks may be modified in other implementations consistentwith the principles of the present disclosure. Further, non-dependentblocks may be performed in parallel. While exemplary embodiments havebeen described herein with respect to a multi-frequency multi-RAT system(MFMRAT), the exemplary embodiments may be applied in multi-frequencyand single frequency multi-RAT systems and in multi-frequency single-RATsystems. In examples described herein, an LTE system was assumed to be amain RAT of the multi-RAT system. However, any RAT in network(s) 130 maybe implemented as the main RAT of the multi-RAT system and can,therefore, exercise the proposed MRAC scheme on behalf of the entiresystem. The use of cross-layer communication for obtaining resourcestatus information and the global flag for maintaining resource statusinformation may also be adapted for use in load balancing in additionto, or instead of, multi-RAT admission control.

Aspects of the present disclosure may also be implemented in methodsand/or computer program products. Accordingly, the present disclosuremay be embodied in hardware and/or in software (including firmware,resident software, microcode, etc.). Furthermore, the present disclosuremay take the form of a computer program product on a computer-usable orcomputer-readable storage medium having computer-usable orcomputer-readable program code embodied in the medium for use by or inconnection with an instruction execution system. The actual softwarecode or specialized control hardware used to implement the embodimentsdescribed herein is not limiting of the present disclosure. Thus, theoperation and behavior of the embodiments were described withoutreference to the specific software code—it being understood that one ofordinary skill in the art would be able to design software and controlhardware to implement the aspects based on the description herein.

Furthermore, certain portions of the present disclosure may beimplemented as “logic” that performs one or more functions. This logicmay include hardware, such as an application specific integrated circuitor field programmable gate array, or a combination of hardware andsoftware.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the present disclosure. In fact, many of thesefeatures may be combined in ways not specifically recited in the claimsand/or disclosed in the specification.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, components or groups but does not precludethe presence or addition of one or more other features, integers, steps,components or groups thereof.

No element, act, or instruction used in the present application shouldbe construed as critical or essential to the present disclosure unlessexplicitly described as such. Also, as used herein, the article “a” isintended to include one or more items. Where only one item is intended,the term “one” or similar language is used. Further, the phrase “basedon” is intended to mean “based, at least in part, on” unless explicitlystated otherwise.

What is claimed is:
 1. A method implemented in a node of a multipleradio access technology (multi-RAT) system, comprising: acquiringresource status information associated with each RAT of the multi-RATsystem; and maintaining an N-bit global flag representing an overallresource availability of the multi-RAT system, based on the acquiredresource status information, for use in admission control; wherein theN-bit global flag is encoded such that each of its N bits describes eachof the multiple RATs.
 2. The method of claim 1, wherein the global flagis associated with a pre-defined set of overall resource availabilitystates of the multi-RAT system, and wherein the availability states aredefined in terms of admission control decisions.
 3. The method of claim1, wherein each of the RATs of the multi-RAT system comprisesmulti-frequency or single frequency RAT systems.
 4. The method of claim1, where the multi-RAT system includes two or more of an evolvedUniversal Mobile Telecommunications System Terrestrial Access Network(E-UTRAN) Frequency Division Duplexing (FDD) system, a E-UTRAN TimeDivisional Duplexing (TDD) system, a Wide Band Code Division MultipleAccess (WCDMA) system, an advanced E-UTRAN TDD system, an advancedE-UTRAN FDD system, a UTRAN TDD system, a high rate packet data (HRPD)system, a Global System for Mobile Communications (GSM) system, and acdma2000 system.
 5. The method of claim 1, wherein portions of each ofthe RATs of the multi-RAT system are deployed in multiple, co-locatedbase stations.
 6. The method of claim 1, wherein portions of each of theRATs of the multi-RAT system are deployed in a single base station.
 7. Anode in a multiple radio access technology (multi-RAT) system,comprising processing circuitry configured to: acquire resource statusinformation associated with each RAT of the multi-RAT system; maintainan N-bit global flag representing an overall resource availability ofthe multi-RAT system based on the acquired resource status information,for use in admission control; and determine whether or not to performadmission control for a system access request based on the overallresource availability represented by the global flag.
 8. The node ofclaim 7, wherein the global flag is associated with a pre-defined set ofoverall resource availability states of the multi-RAT system, andwherein the availability states are defined in terms of admissioncontrol decisions.
 9. The node of claim 7, wherein the multi-RAT systemincludes two or more of an evolved Universal Mobile TelecommunicationsSystem Terrestrial Access Network (E-UTRAN) Frequency Division Duplexing(FDD) system, a E-UTRAN Time Divisional Duplexing (TDD) system, a WideBand Code Division Multiple Access (WCDMA) system, an advanced E-UTRANTDD system, an advanced E-UTRAN FDD system, a UTRAN TDD system, a highrate packet data (HRPD) system, a Global System for MobileCommunications (GSM) system, and a cdma2000 system.
 10. The node ofclaim 7, wherein the multi-RAT system includes a multi-frequency RAT anda single frequency RAT.